An electric heater is activated by an electric supply to heat ambient air, and is used for various purposes. For example, the electric heater is utilized for a laundry dryer or a washing machine having washing and drying functions.
FIG. 1 is a cross sectional view of a conventional combined laundry washing/drying machine, in which a drum-type washing machine having a drying function is shown. The combined laundry washing/drying machine includes a tub 2 supported by a damper 7 and a spring 6 in a body 1 for storing washing water, a washing drum 3 for washing, rinsing and dehydrating the laundry, a motor 4 disposed under the tub 2 for transmitting a rotary force to the washing drum 3, and a pulley and belt 5 disposed between the motor 4 and a drum shaft (not shown) for transmitting the rotary force of the motor 4 to the drum shaft.
The tub 2 is provided at an outward proper position thereof with a blast duct 8 communicated with the washing drum 3. A blast fan 9 compulsorily circulates the air within the blast duct 8, and a heater assembly 10 is disposed at the front of the blast fan 9 to heat the air supplied to the washing drum 3.
With the structure of the combined laundry washing/drying machine as described above, after a series of washing, rinsing and dehydrating processes are completed, the washing drum 3 is rotated at a low speed to uniformly mix the laundry. At that time, a power is supplied to the heater assembly 10 and the blast fan 9, so that the heater assembly 10 generates heat, thereby heating the air. The heated air is circulated within the washing drum 3 and the blast duct 8 to dry the laundry.
FIGS. 2 to 4 show the structure of another conventional heater assembly, in which the heater assembly is enclosed by a housing 11. The housing 11 includes a bottom plate 12, and side plates 13 and 14 vertically extended from both edges of the bottom plate 12. Mounting taps 15 are formed on upper ends of the side plates 13 and 14, and the housing 11 is mounted to the blast duct 8 by the mounting taps 15.
An interior space of the housing 11 is divided into upper and lower halves by a metallic supporting plate 16. The supporting plate 16 is fixed to the side plates 13 and 14, with protruding arms 17 formed at both ends of the supporting plate inserted into penetrating holes of the side plates.
The supporting plate 16 is provided with a heater coil 18 for generating heat by use of electric resistance produced by flowing electric current through the coil. The heater coils 18 are disposed in several rows on upper and lower portions of the supporting plate 16, with the respective heater coils elongated in left and right directions of the supporting plate. The heater coils 18 are electrically connected to each other, and terminals 19 are provided at both ends of the heater coil 18 to supply the power to the heater coil.
The heater coil 18 is supported by an insulator 20 fixed to the supporting plate 16. The insulator 20 is made of insulation material to electrically isolate the heater coil 18 from the supporting plate 16 and support the heater coil against the supporting plate 16. The insulator 20 generally penetrates the supporting plate 16, and has an upper portion protruded upward from the supporting plate 16 and a lower portion protruded downward from the supporting plate, with the portions of the insulator which are upward and downward protruded from the supporting plate are symmetrical to each other.
FIG. 4 shows the structure of the insulator, in which the heater coil 18 is supported by the insulator 20. The insulator 20 of heat insulating material is formed in a plate shape, with an upper end of the insulator being symmetrical to a lower end thereof. Therefore, it will be described on the construction of the upper end only.
The insulator 20 has at both ends parallel notches 21 for mounting the insulator to the supporting plate 16. Also, the insulator 20 has straight slots 22 upwardly and downwardly formed from a center of the upper surface of the insulator. Each of the straight slots 22 has a length equal to the half of the length between the parallel notches. The straight slot 22 is provided at a lower end with a fixing notch 24 for fixing the heater coil 18.
The insulator 20 has at the upper surface thereof inclined guide surfaces 23. The inclined guide surface 23 is to guide a process of insulating the heater coil 18 into the insulator 20. The insulator 20 has lateral notches 25 each formed at both sides thereof. Each of the lateral notches 25 has an inclined angle similar to the inclined guide surface 23. The lateral notch 25 is flush with the fixing notch 24.
It will now be described on the process of insulating the heater coil 18 into the insulator 20 in brief. Adjacent first, second and third convolutions 18a, 18b and 18c of the heater coil 18 are inserted into the fixing notch 24 and two lateral notches 25 of the insulator 20, respectively. Specifically, the first convolution 18a is disposed at a position corresponding to the straight slot 22, while the second and third convolutions 18b and 18c are disposed at the guide surface 23 of the insulator 20, respectively.
Next, the heater coil 18 is pressed, such that the respective convolutions 18a, 18b and 18c is moved in an arrow direction. The respective convolutions 18a, 18b and 18c is guided along the straight slot 22 and the guide surface 23, and is inserted and fixed to the fixing notch 24 and the lateral notches 25.
The respective second and third convolutions 18b and 18c is deformed in a direction away from the first convolution 18a along the guide surface 23, and when it comes in contact with the lateral notch 25, is restored into its original shape to catch the lateral notch.
The conventional heater coil has some problems as follows.
First, the heater coil 18 generates a lot of heat during operation, thereby increasing a temperature of the heater coil, while the heater coil is maintained at a room temperature during no operation. This means the repeated expansion and contraction of the heater coil 18. However, the first, second and third convolutions 18a, 18b and 18c of the heater coil which are secured to the insulator 20 cannot expand and contract, contrary to other portions. The first, second and third convolutions 18a, 18b and 18c, however, receive more thermal stress than other portions of the heater coil receive, so that this phenomenon exerts an advert influence on the heater coil in the strength aspect. In addition, the heat is not uniformly distributed over the total heater coil 18.
Secondly, it is significantly complicate to mount the heater coil 18 to the insulator 20. Specifically, in order to insert the heater coil into the insulator 20, the first, second and third convolutions 18a, 18b and 18c must be inserted into the fixing notch 24 and the lateral notches 25 at the same time. At that time, the elastic direction of the resilience second 18b is counter to that of the third convolution 18c, as shown in FIG. 4. Accordingly, an operator has to guide and press the second and third convolutions 18b and 18c using his/her fingers, with both ends of the first, second and third convolutions 18a, 18b and 18c to be inserted into the insulator 20 being griped by both bands. Such an operation is very complicate, and if it is not careful, the first, second and third convolutions 18a, 18b and 18c are deformed. At this case, the supporting state of the heater coil 18 gets worse.